Power electronics component

ABSTRACT

The invention relates to a power electronics component that comprises a planar ceramics substrate ( 2 ) on whose one face condutor tracks ( 6 ), applied in thick-film technique, are disposed for electrically connecting electrical power components ( 7 ) of a circuit that are also disposed on the ceramics substrate ( 2 ). The ceramics substrate ( 2 ), with its other face, is brazed onto a metal support element ( 1 ) that serves as a heat spreader. The support element ( 1 ) is linked with a thermoconducting housing part ( 9 ) of a housing that accommodates the support element ( 1 ) in a thermoconductive manner. On the face of the support element ( 1 ) facing away from the ceramics substrate ( 2 ), approximately opposite the ceramics substrate ( 2 ), a second ceramics substrate ( 4 ) is brazed onto the ceramics substrate ( 2 ) that carries the circuit and has approximately the same dimensions.

[0001] The invention relates to a power electronics unit, in particularfor a control device in a motor vehicle, with a planar ceramicsubstrate, on one side of which conductor tracks are provided using thethick-film technique for electrically connecting electrical powercomponents of a circuit that are likewise arranged on the ceramicsubstrate and which is brazed by its other side onto a metal supportelement serving as a heat spreader, the support element being connectedin a thermally conducting manner to a thermally conducting housingcomponent of a housing accommodating the support element.

[0002] With power electronics units there is the problem that theelectrical power components generate heat, which has to be removed. Forthis purpose, it is known to form the support element as a planarceramic substrate, on which conductor tracks are provided using athick-film technique, and the electrical power components and anycontrol components there may be are connected to the conductor tracks bysoft soldering. The ceramic substrate is brazed to a metal supportelement, which serves as a heat spreader and is connected to a thermallyconducting housing component by means of an adhesive.

[0003] On account of the different coefficients of expansion of thesupport element and the ceramic substrate, these components deform todiffering degrees, which can have the effect during cooling afterbrazing that the ceramic substrate is damaged and later the soft-solderconnections between the conductor tracks and the electrical powercomponents are possibly also damaged.

[0004] The object of the invention is therefore to provide a powerelectronics unit of the type stated at the beginning which ensures goodheat removal of the heat generated by the electrical power componentsand with which instances of damage caused by the different coefficientsof expansion of the materials of the ceramic substrate and the supportelement are avoided.

[0005] This object is achieved according to the invention by brazingonto the side of the support element that is facing away from theceramic substrate, approximately opposite from said ceramic substrate, asecond ceramic substrate of approximately the same dimensions as theceramic substrate bearing the circuit.

[0006] By brazing approximately identical ceramic substrates onto bothsides of the support element, approximately identical, but opposingthermal stresses are produced from both sides of the support element,compensating one another at least to a great extent and so avoidingthermal-stress-induced damage to the ceramic substrate bearing thecircuit. In this case, the brazing of the two ceramic substrates isperformed as far as possible without interim cooling.

[0007] The form according to the invention has the further effect thatthere is very good dissipation of the heat generated by the electricalpower components, since this heat is transferred very well via thebrazed connection from the ceramic substrate to the support element,which has good thermal conduction and serves as a heat spreader, and isdistributed there over a relatively large surface area before thefurther heat removal to the housing component and to the surroundingstakes place. A reduction of the heat removal caused by an adhesive bondwith respect to the housing component is avoided.

[0008] The support element may consist of aluminum, the heat removalbeing improved further by it being formed from pure aluminum, on accountof its higher thermal conductivity.

[0009] If in this case both ceramic substrates have a layer ofthick-film material on their surface area that is to be brazed, withnickel plating on the free surfaces of said layer, the high temperaturesof the brazing processes do not impair the support element made ofaluminum, which has a relatively low melting point.

[0010] Even more favorable heat removal, and consequently heatspreading, are obtained if the support element consists of copper, whichhas a very high thermal conductivity.

[0011] One or both ceramic substrates may consist of Al₂O₃.

[0012] To obtain optimum heat transfer from the ceramic substrate to thesupport element, the ceramic substrates may be connected to the supportelement by brazing over their entire surface areas, at least to a greatextent.

[0013] A connection which is both simple and has good heat conduction isachieved by the support element having a greater surface area extentthan the ceramic substrates and being connected to the housing componentby its regions that protrude beyond the ceramic substrates restingentirely or partly flat against it.

[0014] In order also to use the surface area of the second ceramicsubstrate for dissipating the heat of the electrical power components,the second ceramic substrate may be in contact with the housingcomponent by its side that is facing away from the support elementresting flat against it.

[0015] For easy mounting of the support element bearing a ceramicsubstrate on both sides, the second ceramic substrate may protrude intoa recess of the housing component corresponding approximately to itsdimensions.

[0016] The heat transfer from the second ceramic substrate to thehousing component is improved still further if a layer of thermallyconductive paste is arranged between the second ceramic substrate andthe housing component.

[0017] An arrangement of the support element on the housing componentthat is both secure and can be simply carried out is achieved by thesupport element being arranged on the housing component by means offastening elements, it being possible for the support element to befastened on the housing component in a simple manner by means of screws.

[0018] In addition, a layer of thermally conductive paste may bearranged between the support element and the housing component, furtherimproving the heat transfer from the support element to the housingcomponent.

[0019] To achieve particularly good heat removal to the surroundings,the housing component may be an outer wall of the housing.

[0020] If the heat that is generated by the electrical power componentsand is to be removed is particularly great, the housing component may bea wall of the housing that can be subjected to a cooling agent.

[0021] An exemplary embodiment of the invention is represented in thedrawing and described in more detail below. The single FIGURE of thedrawing shows a cross section of a power electronics unit.

[0022] The power electronics unit represented has a rectangular supportelement 1 made of pure aluminum, on the upper side of which a firstplanar ceramic substrate 2 is brazed over its entire surface area bymeans of a layer of hard solder 3.

[0023] On the underside of the support element 1, opposite from theceramic substrate 2 and having the same dimensions, a second ceramicsubstrate 4 is likewise brazed by means of a layer of hard solder 5.

[0024] After these two brazing operations, carried out without interimcooling, a thick-film technique was used to provide the ceramicsubstrate 2 with conductor tracks 6, which serve for electricallyconnecting electrical power components 7, in this case transistors, andform a circuit with them. The electrical power components 7 areconnected in a conducting manner to the conductor track 6 by means ofsoft solder 8, and are consequently fastened on the ceramic substrate 2.

[0025] This structural unit is connected to a housing component 9 of analuminum diecast housing in such a way that the support element 1, whichhas a greater surface area extent than the ceramic substrates 2 and 4,rests flat against the housing component 9 with its regions 10 thatprotrude beyond the ceramic substrates 2 and 4.

[0026] Formed in the housing component 9 is a recess 11, whichcorresponds approximately to the dimensions of the second ceramicsubstrate 4 and into which the second ceramic substrate 4 protrudes.

[0027] Arranged between the regions 10 that protrude beyond the ceramicsubstrates 2 and 4 and the housing component 9 is a layer of thermallyconductive paste 12 and between the second ceramic substrate 4 and thebottom of the recess 1 a further layer of thermally conductive paste 13.

[0028] In the regions 10, the support element 1 is securely connected tothe housing component 9 by means of screws 14.

1-15. (canceled)
 16. A power electronics unit for a control device in amotor vehicle, comprising: a housing having a thermally conductinghousing component; a metal support element having first and secondopposing sides; a first ceramic substrate having a connected side and afree side, said connected side facing said first side of said metalsupport element and brazed onto said first side of said metal supportelement; a circuit having conductor tracks and electrical powercomponents arranged on said free side of said first ceramic substrate;and a second ceramic substrate having approximately the same dimensionsas said first ceramic substrate, said second ceramic substrate having aconnected side and a free side, said connected side of said secondceramic substrate facing said second side of said metal support elementand brazed onto said second side of said metal support elementapproximately opposite said first ceramic substrate.
 17. The powerelectronics unit of claim 16, wherein said metal support element is madeof aluminum.
 18. The power electronics unit of claim 16, wherein saidmetal support element is made of pure aluminum.
 19. The powerelectronics unit of claim 17, further comprising a layer of thick filmmaterial on the connected sides of said first and second ceramicsubstrates brazed onto said metal support element and nickel plating onthe free sides of said first and second ceramic substrates.
 20. Thepower electronics unit of claim 16, wherein said metal support elementis made of copper.
 21. The power electronics unit of claim 16, whereineach of said first and second ceramic substrates is made of Al₂O₃. 22.The power electronics unit of claim 16, wherein said first and secondceramic substrates are connected to said metal support element bybrazing over the entire portion of the surface area of the connectedsides facing the metal support element.
 23. The power electronics unitof claim 16, wherein said metal support element has a greater surfacearea than said first and second ceramic substrates and includes regionsextending beyond the area between said first and second ceramicsubstrates, wherein said metal support element is connected to saidthermally conducting housing component by said regions extending beyondthe area between said first and second substrates which rest at leastpartially on said thermally conducting housing component.
 24. The powerelectronics unit of claim 16, wherein said free side of said secondceramic substrate rests flat against said metal support element.
 25. Thepower electronics unit of claim 24, wherein said thermally conductinghousing component defines a recess in which said second ceramicsubstrate is at least partially received.
 26. The power electronics unitof claim 16, further comprising a layer of thermally conductive pastearranged between said second ceramic substrate and said thermallyconducting housing component.
 27. The power electronics unit of claim16, further comprising fastening elements connecting said metal supportelement to said thermally conducting housing component.
 28. The powerelectronics unit of claim 27, wherein said fastening elements comprisethreaded elements.
 29. The power electronics unit of claim 16, furthercomprising a layer of thermally conductive paste arranged between saidmetal support element and said thermally conducting housing component.30. The power electronics unit of claim 26, further comprising anotherlayer of thermally conductive paste arranged between said metal supportelement and said thermally conducting housing component.
 31. The powerelectronics unit of claim 16, wherein said thermally conducting housingcomponent comprises an outer wall of said housing.
 32. The powerelectronics unit of claim 16, wherein said thermally conducting housingcomponent comprises a wall arranged for receiving a cooling agent.